1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to improvements in prosthetic feet.
2. Description of the Prior Art
During normal ambulation, the first part of a foot to contact the ground is the free end of the heel. This initial contact between heel and ground is known as the xe2x80x9cheel strike.xe2x80x9d The free end of the heel is soft and thus cushions the heel strike to at least some extent. The hard bottom of the heel is the next part of the foot to strike the ground; its hardness allows it to support the entire weight of the body. The foot continues to rotate in the well-known way until the toes xe2x80x9cpush offxe2x80x9d at the end of a step.
Early prosthetic feet were quite rigid and provided little or no cushion to the impact on the ground at the moment of xe2x80x9cheel strikexe2x80x9d and little or no elastic response at xe2x80x9cpush off.xe2x80x9d The shock of impact was thus transmitted directly to the skeletal structure of the user, and the lack of elastic response forced an unnatural gait.
Perhaps the earliest prosthetic foot that provided an elastic response at heel strike and push off is disclosed in U.S. Pat. No. 4,547,913 to Phillips, assigned to Flex Foot, Inc. Multiple versions of that device have been developed. The original version is formed of a carbon fiber epoxy matrix consisting of a one-piece combination pylon upper and a one-piece sole. Mechanical fasteners interconnect the upper and the sole. In a second embodiment, the pylon is a round hollow tube and is connected by mechanical fasteners to a rectangular-shaped upper. A third version is like the first except that a standard Sach(copyright) foot adapter is employed to connect a standard prosthetic pylon. A fourth version is like the third but has a slightly different geometry. In a fifth version, an elastomeric glue connects the upper and the sole. In additional embodiments, leaf springs or hydraulic cylinders are incorporated into the prosthetic foot.
Although the developments in the art since the mid 1980s have significantly advanced the technology of prosthetic feet, the known prosthetic feet still provide little or no heel elasticity in a direction parallel to the ground. Instead, they provide elastic response in a vertical plane. Thus, although the impact at heel strike is reduced vis a vis the pre-1980""s prosthetic feet, the reduced impact is transmitted vertically to the skeletal structure of the user, and the elastic response in a vertical plane causes a four to six millimeter bounce at heel strike. This vertical response causes an unnatural walk because a healthy human heel is soft at the back or free end where heel strike occurs and is hard on the bottom so that it can support the entire weight of the body. Thus, the normal gait of a human includes a rolling motion as the back of the heel strikes the ground; there is no vertical motion causing the heel to bounce upon ground impact. Accordingly, there remains a need for a prosthetic foot that provides substantial heel elasticity in a direction parallel to the ground.
A healthy human foot rolls on the lateral part of the foot during ambulation. The medial part of the foot provides a cushion and the force required at push off. Thus, there is a smooth transition from heel strike to push off, with no vertical dynamic response of the type that could cause the foot to bounce. Prosthetic feet of the type heretofore known, however, do not provide a smooth transition from heel strike to push off. This lack of a smooth transition produces what is known in the industry as a xe2x80x9cflat spot.xe2x80x9d The presence of a flat spot between heel strike and push off produces an unnatural gait.
More particularly, the dynamic response is primarily vertical at the heel and the toe of a prosthetic foot. There is little or no component of the dynamic response in a horizontal plane as present in a healthy natural foot. The absence of dynamic response in a horizontal plane results in a step like motion going from an elastic vertical motion at heel strike to little or no support at mid-stance (the flat spot), and then again to an elastic vertical motion at push off.
There is a need, therefore, for a prosthetic foot having a dynamic response in a horizontal plane during heel strike, that provides a smooth transition between heel strike and push off to eliminate the flat spot, and that provides a dynamic response in a horizontal plane during push off.
The human foot provides a more rigid support laterally than medially. This design is advantageous because when an instability occurs, the weight of the person shifts from the rigid outer or lateral edge of the foot to the less rigid inner or medial edge. In this way, the prosthetic foot takes advantage of the presence of the natural foot, i.e., the lateral-to-medial motion experienced at the moment of an instability shifts additional support duties to the natural foot. One major drawback of the heretofore known prosthetic feet is the fact that such feet provide an exactly vertical response during ambulation with no component toward the medial section of the foot. Thus, if an instability in one foot urges the person to fall away from the natural foot, there is no shift of weight toward the medial part of the prosthetic foot as would occur in a natural foot, and the likelihood of a fall is substantially increased.
A prosthetic foot is therefore needed that has differentiated medial and lateral stiffness so that it can respond to instabilities in much the same way as a natural foot.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The long-standing but heretofore unfulfilled need for a dynamic prosthetic foot is now met by a new, useful, and nonobvious prosthetic foot having multiple load points and a pair of upper sections that are divided into an anterior upper section and a posterior upper section. The novel prosthetic foot includes a sole having a heel end and a toe end that are in substantially coplanar relation to one another and a pair of upper sections disposed normal to the sole. The upper sections are formed by longitudinally splitting an upper member having a heel end, a toe end, and a pair of flat, transversely spaced apart, pylon supports formed in its heel end. A first upper section is positioned toward the toe end of the foot in anterior relation to a second upper section that is positioned toward the heel end of the foot in posterior relation to the anterior section.
The heel end of each upper section has a gradual ninety degree bend formed therein so that the pylon supports are disposed substantially perpendicular to the sole. A transversely disposed parting line is formed where each pylon support separates from the sole.
Each pylon support is formed integrally with its associated upper section. The pylon supports include a lateral, anterior pylon support and a medial, posterior pylon support. An elongate slot is formed in the heel end of the upper member, substantially coincident with a longitudinal axis of the prosthetic foot. The slot extends from an uppermost end of the heel end of the upper member to a preselected point that is about two-thirds of the way from the heel of the sole to the toe of the sole.
Forces acting on the lateral pylon support are substantially confined to the lateral section of the upper member and forces acting on the medial pylon support are substantially confined to the medial section of the upper member.
Moreover, forces applied to the lateral, anterior pylon support are shifted in a posterior direction to the medial, posterior pylon support to mimic the operation of the fibula and tibia in a natural leg. The lateral, anterior pylon support performs the function of a fibula and the medial, posterior pylon support performs the function of a tibia. The lateral, anterior pylon support has a greater thickness than the medial, posterior pylon support and the medial member. The greater thickness imparts greater stiffness so that forces applied to the lateral, anterior pylon support and the medial, posterior pylon support are transferred more to the medial, posterior pylon support and medial section of the upper member than to the lateral, anterior pylon support and lateral section of the upper member, thereby mimicking the reaction of a natural foot to forces applied thereto.
The sole has a first convexity formed in the heel end that performs the function of the bottom of a natural heel. The sole has a concavity longitudinally spaced from the first convexity, said concavity performing the function of a natural arch. The sole has a second convexity longitudinally spaced from the concavity, said second convexity performing the function of the ball of a natural foot. The transverse parting line where the pylon supports separates from the sole are positioned in substantial juxtaposition with said concavity.
The elongate slot that divides the upper member into two upper sections has a heel end that is in open communication with the respective free ends of the lateral, anterior and medial, posterior pylon supports. The leading end of the slot extends to the point of inflection where the concavity formed in the sole meets the second convexity.
Pylon connectors are secured to the respective trailing sides of the pylon supports and elongate pylons are joined thereto.
In an alternative embodiment, the upper sections between the transverse parting line and the toe end of the sole are formed integrally with one another.
In a second embodiment of the invention, elongate pylons supplant the pylon supports and connectors.
An important object of the invention is to provide a prosthetic foot having a smooth transition from heel strike to push off.
Yet another object is to provide a prosthetic foot having differentiated medial and lateral stiffness so that an instability tends to shift weight from the lateral edge of the prosthetic foot to the medial edge thereof, just as in a natural foot.
Another important object is to provide a dynamic prosthetic foot having connections to pylons that mimic the actions of a natural fibula and tibia.
Yet another object is to provide multiple pylon supports (first embodiment) or pylons (second embodiment) exhibiting lower torsional stiffness when compared to a single tube-type pylon support or pylon, respectively.
Another object is to provide a prosthetic foot that flexes in the medial lateral planes without having any moving surfaces, i.e. , parts that wear and make noise when two surfaces move relative to each other, such as in a bushing or in a hinge.
Another important object is to provide a prosthetic foot having an improved rollover motion.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.